Title 23

SECTION 1340.9

1340.9 Computation of estimates.

§ 1340.9 Computation of estimates.

(a) Data used. Except as otherwise provided in this section, all data collected pursuant to § 1340.7(e) shall be used, without exclusion, in the computation of the Statewide seat belt use rate, standard error, and nonresponse rate.

(b) Data editing. Known values of data contributing to the Statewide seat belt use rate shall not be altered in any manner.

(c) Imputation. Unknown values of variables shall not be imputed unless NHTSA has approved the State's imputation procedure prior to data analysis.

(d) Sampling weights. The estimation formula shall weight observed data by the sampling weights as required by the sample design and any subsequent adjustments.

(e) Sampling weight adjustments for observation sites with no usable data. States shall include a procedure to adjust the sampling weights for observation sites with no usable data, including observation sites where no data were collected and observation sites where data were discovered to be falsified.

(f) Nonresponse rate. (1) Subject to paragraph (f)(2) of this section, the nonresponse rate for the entire survey shall not exceed 10 percent for the ratio of the total number of recorded unknown values of belt use to the total number of drivers and passengers observed.

(2) The State shall include a procedure for collecting additional observations in the same calendar year of the survey to reduce the nonresponse rate to no more than 10 percent if the nonresponse rate in paragraph (f)(1) of this section exceeds 10 percent.

(g) Variance estimation. (1) Subject to paragraph (g)(2) of this section, the estimated standard error, using the variance estimation method in the survey design, shall not exceed 2.5 percentage points.

(2) If the standard error exceeds this threshold, additional observations shall be conducted in the same calendar year of the survey until the standard error does not exceed 2.5 percentage points.

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